1. Field of the Invention
The present invention relates generally to assemblies for interconnecting optical fibers, and more specifically, to fiber optic receptacle and plug assemblies including an alignment sleeve insert with alignment and keying features for interconnecting optical fibers within a fiber optic communications network.
2. Technical Background
Optical fiber is increasingly being used for a variety of broadband applications including voice, video and data transmissions. As a result, fiber optic communications networks include a number of interconnection points at which optical fibers are interconnected with other optical fibers. Fiber optic networks also include a number of connection terminals, examples of which include, but are not limited to, network access point (NAP) enclosures, aerial closures, below grade closures, pedestals, optical network terminals (ONTs) and network interface devices (NIDs). In certain instances the connection terminals include connector ports, typically opening through an external wall of the terminal, that are used to establish optical connections between optical fibers terminated from the distribution cable and respective optical fibers of one or more pre-connectorized drop cables, extended distribution cables, tether cables or branch cables, collectively referred to herein as “drop cables.” The connection terminals are used to provide communications services to a subscriber. In this regard, fiber optic networks are being developed that deliver “fiber-to-the-curb” (FTTC), “fiber-to-the-business” (FTTB), “fiber-to-the-home” (FTTH) and “fiber-to-the-premises” (FTTP), referred to generically as “FTTx.”
Conventional connector ports opening through an external wall of a connection terminal typically include a receptacle for receiving a connectorized optical fiber, such as a pigtail, optically connected within the connection terminal to an optical fiber of the distribution cable, for example in a splice tray or splice protector. At present, these receptacles are relatively large in size because the connection terminal in which they are located does not limit the size of the receptacle. Furthermore, existing receptacles include a two-piece receptacle housing defining an interior cavity that houses a biased alignment sleeve for receiving and aligning the mating ferrules. As previously mentioned, one of the mating ferrules is mounted upon the end of an optical fiber that is optically connected to an optical fiber of the distribution cable within the connection terminal. The other mating ferrule is mounted upon the end of an optical fiber of a drop cable that extends into the receptacle from outside the connection terminal. The alignment sleeve of the receptacle assists in gross alignment of the ferrules, and ferrule guide pins or other alignment means assist in more precise alignment of the opposing end faces of the ferrules.
In particular, a fiber optic plug mounted upon the end of a fiber optic drop cable is received within the receptacle through the external wall of the connection terminal. Typically, the plug includes a generally cylindrical plug body and a fiber optic connector including a plug ferrule disposed within the cylindrical plug body. The end of the cylindrical plug body is open, or is provided with one or more openings covered by a removable cap, so that the ferrule is accessible. The plug ferrule is mounted upon one or more optical fibers of the fiber optic drop cable such that mating the plug with the receptacle aligns the optical fibers of the drop cable with respective optical fibers terminated from the distribution cable within the connection terminal. In the process of mating the plug with the receptacle, the plug ferrule is inserted into one end of the alignment sleeve housed within the receptacle. As a result of the construction of a conventional fiber optic plug, the alignment sleeve is minimally received within the open end of the plug body as the plug ferrule is inserted into the alignment sleeve.
Several different types of conventional fiber optic connectors have been developed, examples of which include, but are not limited to, SC, ST, LC, DC, MTP, MT-RJ and SC-DC connectors. The size and shape of each of these conventional connectors are somewhat different. Correspondingly, the size and shape of the alignment sleeve, the receptacle and the plug are somewhat different. As a result, in conventional practice different fiber optic receptacles and plugs are utilized in conjunction with the different types of fiber optic connectors. In this regard, the fiber optic receptacles generally define different sized internal cavities corresponding to the sizes of the alignment sleeve and, in turn, according to a ferrule of the fiber optic connector to be inserted within the alignment sleeve.
In addition to requiring the use of different fiber optic receptacles and plugs based upon the specific type of optical connector, conventional receptacle and plug assemblies are relatively large in size. More compact and organized assemblies are needed for high-density installations. Current smaller sized assemblies, however, are not able to satisfy the high tensile loads required for FTTx installations, including for example the 600 lbs. drop cable pull test requirement. Exposure to adverse environmental conditions is also a significant concern since current network plans suggest that receptacles may remain unoccupied (without a mated plug) for an extended period of time due to initial service (also referred to as “take rates”) being less than total capacity. Based on tensile load requirements and the need for prolonged environmental protection, it would be desirable to provide a fiber optic receptacle and corresponding fiber optic plug suitable for foolproof mounting in a connection terminal or similar enclosure defining an external wall through which optical fibers are interconnected. As yet however, there is an unresolved need for a compact, yet sufficiently robust fiber optic receptacle that is configured to receive only a fiber optic plug having the same type of optical fiber connector. There is a further unresolved need for a fiber optic receptacle adapted to accommodate an alignment sleeve insert with alignment and keying features that correspond to complimentary alignment and keying features provided on a fiber optic plug of like ferrule configuration.